专业英语笔记

Volatage attempts to make a current flow, and current will flow if the circuit is complete.电压会使电流流动，如果电路时闭合电路，就会有电流流过。Voltage is a difference between two points,but in electronics we often refer to voltage at a point meaning the voltage difference between that point and a reference point of 0 V.电压是两点间的差值，但在电子学中我们常说的某一点上的电压其实是指这点和零伏参考点之前的一个电压差。Noise is relatively easy to eliminate from digital signals because it is easy to distinguish from the desired signal which can only have particular values.干扰相对较容易从数字电路中去除，因为有用信号只取特定的值，所以干扰就很容易与有用信号区别开。The forward voltage drop of a diode is almost constant whatever the current passing through the diode so they have a very steep characteristic.无论流过二极管的电流时多少，二极管的正向压降几乎总是一个常数，因此二极管有一个非常陡峭的特性Small signal diodes can be damaged by heat when soldering ,but the risk is small unless you are using a germanium diode.焊接时产生的热量损坏小信号二极管，但是除非你用的是锗二极管。The transmitter converts the message into a signal, the form of which is suitable for transmission over the communication channel.发信机把消息转变为信号，信号形式要适合在通信信道中传送。It changes the received signal back into a message and passes the message onto its destination which may be a loudspeaker,teleprinter or computer data bank.它把接收到的信号变回成消息，并把消息传给终端，这个终端可以是一台扬声器、电传打字机或一个计算机数据库。A radio can handle a supergroup provided sufficient bandwidth is available.The size of the group is a compromise as treating each channels individually involves far more equipment because separate filters,modulators and oscillators are required for every channels rather than each group.只有有足够的带宽，无线电可以处理一个超群，群的大小根据每路信号的情况确定，因为处理每一路都需要独立的滤波器、调制器及振荡器。To do this it is necessary to employ synchronized switches at each end of the communication link to enable samples to be transmitted in turn,from each of several circuits.要做到这一点，必须在通信链路的两端采用同步开关，使对来自各条电路的抽样值能依次轮流传送It will be seen later that most of the advantages of digital modulation come from the transmitted pulses having two levels only,this being known as a binary system.以后我们会发现数字调制的大多数优点来自发送的脉冲只有两个电平，这种系统被称为二进制系统。In the telephone system,the use of fiber optics for interconnecting central offices within a metropolitan area and for lower levels in the switching hierarchy is still increasing rapidly.在电话系统中，光纤在主要城市地区中心交换局间互连和低级交换中的使用一直在迅速增加。The third generation mobile communication system(3G)currently being developed in Europe is intended to integrate all the different services of second generation systems and cover a much wider range of broadband services.目前在欧洲正在开发第三代移动通信系统，其目的是要综合第二代系统所有不同业务并覆盖更广泛的业务。The ideal mobile telephone system would operate within a limited assigned frequency band and would seve an almost unlimited number of users in unlimited areas.理想的移动电话系统将在有限的给定频段上工作，但却可以向任意多的地区几乎是任意多的用户提供服务。The mobile station contains atransceiver,an antenna,and control circuitry,and may be mounted in a vehicle or used as a portable hand-held unti.一个移动站包括无线电接收机，天线和控制电路，这种移动台可以安装在传输系统或手机里。The base station serves as a bridge between all mobile users in the cell and connects the simultaneous mobile calls via telephone lines or microwave links to the MSC.这些基站在所有的蜂窝移动用户间建立了一座桥梁，通过电话线或微波连到MSC，基站把同步移动电话连接起来。ATM allocates bandwidth on demand by constructing virtual channels and virtual paths between source and destination points on the ATM network boundaries.ATM通过在其网络边界内的起点和终点之间建立虚拟信道和虚拟通路，按需分配带宽。The most inportant of these components is the central processing unit(CPU),or microprocessor,which acts as the”brain” of your computer.这些元件中最重要的是作为计算机“脑袋”的中央处理器，或叫微处理器Because hard disks can hold massive amounts of intormation,they usually serve as your computers primary means of storage,holding almost all of your programs and files.因为硬盘可以容纳大量信息，它们通常用计算器上的主要存储器保存几乎全部程序和文件。When you want to select an item,you point to the item and then click(press and release)the primary button.如果要选择某个内容，先指向该内容，然后“单击”（按下再放开）主按钮。Both types ptoduce sharp images,but LCD monitors have the advantage of being much thinner and lighter.CRT monitors,however,are generally more affordable.两种类型都可产生清晰图像，但LCD显示器具有较薄和较轻的优势，但是，CRT显示器通常价格较低廉。They can print in black and white or in full color and can produce high-quality photographs when used with special paper.它们可以进行黑白或全白打印，使用特殊纸张时，可打印出高质量的照片。LED有红色、橙色、琥珀色、黄色、绿色、蓝色和白色。蓝色和白色的LED比其他颜色的贵的多。LED的颜色由半导体物质决定，而不是包装（塑料）的着色，所有颜色的LED可以用来着色的包装包起来，包装可能是暗淡的（乳白色）或者明亮的（通常描述成透明色）。着色的包装也可以是暗淡的（标准类型）或者透明的。信息源（如语音、数据、视频等）是信息的来源。目的地或接收器（如收音机，电视，传真机，计算机等）是信息传输的终点，记住我们刚刚讨论的，我们现在可以定义电信为从信息源到目的地远距离传递信息的过程，一系列中继设备被用到信息传输中（如调制解调器，编解码器，交换机等）光纤到户是光缆以各种方式进入用户住宅的社区通信基础设施，经过多年的等待以后，光纤到户以多种部署形式最终出现在全美，尽管光纤到户只是一种技术，有趣的是它揭示了本地接入市场的竞争状态，光纤到户网络能够比现在宽带技术提供高很多倍的带宽。现在似乎大家都需要高速数据业务，可靠的语音业务，以及高质量的视频业务，只要服务快速可靠，这些服务通过数字用户线。光纤调制解调器，还是无线架构传递时无关紧要的目前已经出现三代移动电话，每一代都比前一代更加可靠和灵活。你仅仅使用蜂窝进行语音通信，而且只能在国内数字移动电话系统增加了传真，数据，消息还是语音业务，而且能在多个国家使用，多媒体业务为移动设备增加了高速的数据传输服务，允许通过移动电话传输新的视频，音频以及应用其他业务